Steve: Welcome to the Scientific American podcast Science Talk posted on August 7th, 2012. I am Steve Mirsky. As you no doubt know, the Curiosity rover has successfully landed on Mars. Ultimately the plan is to drive Curiosity from its touchdown site in Gale Crater up the slope of a six-kilometer high mountain called Mount Sharp. Along the way, scientists here on Earth will be looking for geological signs of past water and even past life. The instrumentation aboard Curiosity that can do these investigations is called the Mars Science Laboratory. Yesterday, August 6th, Scientific American contributor David Appell talked with Mars Science Lab project leader John Grotzinger. He's also a professor of Geology at Caltech, specializing in sedimentology, stratigraphy, geobiology and ancient surface processes on Earth and Mars. Here’s David with Grotzinger.

Appell: Thanks. I'm sure you're pretty exhausted right now.

Grotzinger: Pretty wiped out, yeah.

Appell: How about just tell me first how you felt last night. I was watching it on the Web; what was it like being there after all your work?

Grotzinger: Well you know, truthfully, it was a lot of other people's work and I, you know, I really get to be a participant as a scientist in a, kind of, a miracle of engineering. You look at this rover, you look at this spacecraft, you see how complex it is, and I think it must be true that not one person can really fathom everything about the rover and everything about the EDL system. And so it requires a group of people to come together and collectively plan it and build it and study it and then fly it. And the way that came together and how flawlessly it worked is just, kind of, a miracle of engineering to me. So, it was thrilling. I felt like, you know, I was there in what will surely be a historic moment for, you know, the success of this technology.

Appell: Was there a lot of tension in the room?

Grotzinger: There was. You know, the thing about it is that it's a trained tension, because you know exactly when the different moments are coming up, when a command sequence is going to be executed; and you know what to listen to, to know that it confirmed, that a confirmation is indicated that it functioned correctly. And the whole thing itself is something that we've practiced many times. So, going into that room and sitting in those seats with all the people and doing practice sessions like that, you at some level, you expect it, you get used to it; but when the actual event is happening is when you realize, you know, just how extraordinary it really is.

Appell: The site you landed on—is there like a particular place on Earth that you would you know identify this with, something that it reminds you of, maybe you've seen before.

Grotzinger: Well, the landing site itself is quite different—Mount Sharp with this five kilometer stack of flat-lying layers. There's nothing quite like that on Earth. There are places where you see even thicker stratographic sections, but because of plate tectonics on Earth, they're usually very deformed and, you know, faulted and folded and stuff like that; or if they're flat lying, they're thin on the order of hundreds of meters rather than kilometers. Where we've landed in the ellipse, at a large scale from orbit, it looks fairly familiar in that it's a feature we call an alluvial fan. And these are the kind of the features that form out in arid climates like Death Valley where it rains only occasionally and builds these deposits. So we think we landed very near the base of one those.

Appell: That black stripe that you mentioned in the press conference today—the dunes, what makes it black, what material is making it black?

Grotzinger: We think from orbit, the imaging spectrometers recognize it as some combination of the minerals olivine and pyroxene. And so we think that, you know, we don't really know what it's made out of till we go over there and analyze it, but we think we're likely to find it will be some significant quantities of olivine and pyroxene.

Appell: How will you decide now where exactly you want to go? What do you do to analyze that?

Grotzinger: Well, we have lots of data from orbit and as the instruments check out, we're going to be getting more data from our own rover; and we put it altogether and look at the patterns that we see from orbit, and we make decisions based on what looks interesting, what looks significant, and most importantly, what hypothesis can we test by analyzing this rock versus that rock? And then, you know, we sort of, look at all these options and then string them together like a chain of pearls and then just go after one after the other. It's a big decision making process; the whole team is involved, everybody gets to have their say, and we talk about it enough that people eventually feel comfortable enough making the decisions.

Appell: Is it pretty dynamic? Can you make changes, you know, day by day?

Grotzinger: Yeah.

Appell: Is there any chance of finding, you know water, contemporary water anywhere in this vicinity of where you've landed and are going to go, or does it appear it's going to be dry and you'll have to analyze the stratiography?

Grotzinger: I think it's going to be pretty dry. We had provided some evidence to the agency that we were not going to land on a place that had ice or water near the surface, and if we ever did find evidence for either one of them, we wouldn't be able to go there until a NASA commission had approved us to do that because we don't want to contaminate an existing water source.

Appell: Is that why you chose to be near the equator?

Grotzinger: No, it just happened that Gale is at a really low elevation there and the more we looked at it, in terms of the details, the more we warmed up to it.

Appell: We've had several rovers on Mars now, so why another rover and why this rover in particular?

Grotzinger: Yeah,you know, I think that the way to think about a rover is the same way that a geologist uses an off-road vehicle here on Earth. You have to go to many different places. You can't just say you’ve done one rover missions and two rover missions and now you're done because really what you're trying to do is analyze the past, the deep geologic past, in terms of major events that influence the evolution of the planet; including those kinds of events that may have created environments that were habitable to microorganisms. And the trick always is that you need to find the best places to go to because you're really not sure of what it is that you might discover something that you're actually looking for.

Appell: And something I've been wondering that I couldn't find: How far up Mount Sharp do you think you'll be able to go and, you know, what angle of incline are you able to go at?

Grotzinger: Yeah, well the whole thing is potentially drivable, and it's shaped like Hawaii—it's quite high in elevation, but that elevation is all dissipated over some pretty gentle slopes. And we'll probably go up to, I would say, you know, probably the first kilometer—where we see a significant change in the planet's history from the time when it formed clays and sulfates to the time when you see that there are just anhydrous minerals there—and so across that boundary and then afterwards look at our data and decide whether it's worth continuing to go up or whether we should go back down and sample a different area on the way down.

Appell: Is there some maximum angle of incline the rover can tolerate?

Grotzinger: Yeah, we have, sort of, a flight limit of about 20 degrees, but we're pretty sure we can handle things up to 25, but that's just margin there.

Appell: How long have you worked on this project since you started?

Grotzinger: For me it's been five years.

Appell: When do you see, you know, sort of, science kicking into high gear and after the commissioning period—how long do you think that'll be?

Grotzinger: You know, I think we'll—after the commissioning, the second half of commissioning—I think we'll be pretty well ready to go. You know it'll probably two to three months out, but once that happens, you know, we'll get the keys.

Appell: So, will you, sort of, be on a little bit of hiatus until then; I mean, not a hiatus, but a little bit in getting-ready-to-go mode, not so much in, you know, attack mode until then?

Grotzinger: We're still going to hit it with all we've got.

Appell: Oh, yeah.

Grotzinger: There are a lot of instruments to get checked out, and before, you know, we need to leave or go some other place, we're pretty confident that we’re going to find a lot of good stuff at where we are.

Appell: If you can—I don't think you can anymore but—how is the situation right now compared to what you might have expected, you know, yesterday or week ago or a month ago? Can you give me a sense of that?

Grotzinger: Oh yeah, I think, you know, the way that many of us feel today is, a great sense of relief and also a great sense of accomplishment. It's just been something that we've been after for many, many years now and, you know, it just all came home.